Coffee has been a popular drink in the United States for over 100 years. In the 1700's, coffee first found its way to the Americas by means of a French infantry captain who nurtured one small plant on its long journey across the Atlantic. This one plant, transplanted to the Caribbean Island of Martinique, became the predecessor of over 19 million trees on the island within 50 years. It was from this humble beginning that the coffee plant found its way to the rest of the tropical regions of South and Central America.
Coffee production has long been considered a vital part of many national economies. After the Vietnam war, the US helped to stimulate the recovery of the Vietnam economy by supplying farmers with coffee plants to grow. The coffee production of Vietnam subsequently grew so large that it significantly negatively impacted coffee production in South America. Today coffee (in the form of coffee beans) is the second most traded commodity in the world, and coffee production is considered so vital to so many economies that the majority of coffee production in the world is subsidized by governments to allow pricing to be competitive in the world market.
Within the past two decades, “designer” coffees have become more popular. Yearly revenues for up-scale coffee shop such ad Starbucks often exceed $900,000 per shop from the first year, and the Starbucks coffee shops have a total combined revenue greater than $10.7 billion per year. Coffee shops such as Starbucks cater to the up-scale coffee market, where consumers pay handsomely for cups of coffee that deliver subtle variations in flavor which they consider pleasing to the palette, or fashionable, or both.
Coffee (in the form of a drink) is produced by passing hot water through ground coffee beans, so that some of the organic compounds within the coffee beans dissolve into the hot water as it passes through. The process of dissolving organic compounds form coffee beans into water to produce coffee is commonly referred to as brewing. The solubility and stability of the organic compounds which dissolve into the water during the brewing process is temperature-dependent, and thus the flavor and perceived quality of coffee is dependent on the brewing temperature.
Once coffee has been brewed, measuring total dissolved solids (TDS) is one scientific method to measure how “strong” the coffee is. The rate at which these solids (organic compounds) dissolve into the hot water during the brewing process is referred to as the extraction rate.
There are three major classes of coffee-brewing apparatus in use today: home coffee brewers, commercial coffee brewers, and espresso brewers. Home coffee brewers typically heat water to the boiling point in a small chamber, where the periodic rapid expansion of a steam bubble created from boiling water is used to propel small pulses of nearly-boiling water up an open-topped tube. After the nearly-boiling water spurts out of the top of the open-topped tube, the water drips down onto the top of a quantity of coffee grounds contained within a brewing basket. Brewing baskets are designed to allow water to seep down through the grounds and escape through the bottom of the brewing basket, while keeping the grounds contained. Some brewing baskets include micro-fine filters which contain the grounds, and may be cleaned and re-used, while other brewing baskets are designed to be used in conjunction with disposable paper filters, which allow brewed coffee to pass through while containing the grounds. Once brewed coffee has passed through the filter, the brewing process is complete.
Within the coffee industry, the basket containing the grounds and the filter is sometimes referred to as a “brewer”, but within this document, the entire coffee-brewing apparatus (including water-heating apparatus, basket, and filter) may be referred to alternately as a brewer, a coffee machine, or a coffee brewer.
The periodic flash-boiling method used to heat and pump the hot water in home coffee makers produces pulses of water of somewhat varying temperature, whose average temperature varies according to the atmospheric pressure at which the brewer is operated. Atmospheric pressure varies with altitude, so the temperature of the hot water these machines produce is dependent on altitude. The boiling point of water varies with dissolved mineral content, so the brewing temperature of these coffee makers also varies with the dissolved mineral content of the water used.
Commercial coffee makers typically use different means than home coffee makers for controlling the temperature of the hot water. Commercial coffee makers typically include a high-thermal-mass reservoir, either in the form of a block of heated metal, or a chamber of heated water, or both. A thermostat is typically used to turn on a heating element when the sensed temperature of the thermal reservoir drops below a preset value, and to turn that heating element off again when the set temperature of the thermal reservoir rises above a another pre-set value. Such thermostats are typically adjusted mechanically, and commercial coffee makers with such thermostatically controlled thermal reservoirs typically produce hot water whose temperature is regulated within plus or minus 5 degrees Celsius. This hot water is passed through a basket of coffee grounds similar to the baskets used in home coffee machines, to produce brewed coffee. An alternate design used in some commercial coffee makers uses a pressure switch in place of a thermostat. When the water within the thermal reservoir approaches the boiling point, its pressure increases, turning off the heating element.
Since the size of commercial coffee makers may be large compared to home units, and since it is desirable for an even flow of water to flow down through the coffee grounds within the basket, some commercial coffee machines use a perforated inverted cone or the like above the coffee grounds to distribute the flow of hot water over the surface of the grounds during the brewing process.
Due to the thermal mass of their internal heat reservoirs, commercial coffee machines often have a substantial initial warm-up time. There is a need for high-quality well thermally regulated coffee brewing machines with a reduced warm-up time.
Not only do the large thermal reservoirs in commercial coffee makers require a substantial amount of time to heat up, but these coffee makers also typically have considerable size and weight, which requires substantial installation space within a coffee shop. There is a need for more compact commercial coffee making equipment which requires less space in coffee shops.
Commercial coffee brewers are sometimes used to brew an entire pot or large batch of coffee, and they are sometimes used to brew individual cups of coffee. When a multi-cup batch of coffee is brewed, a larger basket and more coffee grounds are used than when an individual cup of coffee is brewed. Some commercial brewers are capable of delivering hot water at different pre-programmed rates, and some can be programmed to deliver a certain quantity of water in a certain amount of time (for instance, to brew a single cup, or a 10-cup batch, etc.). Within such brewers, the flow rate is controlled as a pulse-width-modulated series of bursts of hot water, where within each burst, the hot water is delivered at the same fixed rate. The average flow rate (averaged over more than one burst) is varied by alternately turning a valve on and off, where the ratio of on time to off time determines the flow rate, and the maximum flow rate is achieved when the valve is on all the time. By timing the total amount of on time in a series of such on/off bursts, a total desired quantity of water can be dispensed.
The rate at which water is delivered to the grounds in the basket has some effect on the rate at which water moves through the grounds in the basket. For instance, if a significant head of water builds up on top of the grounds, the flow rate through the grounds increases, and this can change the extraction rate in the brewing process.
Since the extraction rate is known to affect the flavor of brewed coffee, there is a need for innovative technologies which allow baristas to experiment with both water temperature and flow rate in innovative ways. At the time of writing of this patent application, brewing parameters are typically communicated between baristas in terms of water temperature, time, and volume. It is anticipated that specification of additional parameters will develop over time.